Despite having fewer ASD diagnoses, girls with the condition tend to have more of its genetic mutations than boys do. In particular, girls have more large duplications or deletions of DNA, called copy-number variations, in their genome. Older girls diagnosed with autism generally have more severe symptoms than boys, including lower IQ scores. So, if females have more of these variations in their DNA, and genetics are a risk factor for autism, why would fewer girls be given a diagnosis of autism? There may be something protecting girls against symptom severity — a concept that's come to be known as the "female protective effect." But what is this protective effect? Is there a gene that blocks the effect of other genes, or turns on compensatory genes? Does some sort of environmental factor in females, such as the presence of specific hormones, alter the way the autism genes are expressed? Are the genes that control for brain development in boys and girls regulated differently?
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